/*
 * Licensed to ElasticSearch and Shay Banon under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. ElasticSearch licenses this
 * file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.elasticsearch.search.suggest.phrase;

import java.io.IOException;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.util.BytesRef;
import org.elasticsearch.search.suggest.SuggestUtils;
import org.elasticsearch.search.suggest.phrase.DirectCandidateGenerator.Candidate;
//TODO public for tests
public final class LaplaceScorer extends WordScorer {
    
    public static final WordScorerFactory FACTORY = new WordScorer.WordScorerFactory() {
        @Override
        public WordScorer newScorer(IndexReader reader, String field, double realWordLikelyhood, BytesRef separator) throws IOException {
            return new LaplaceScorer(reader, field, realWordLikelyhood, separator, 0.5);
        }
    };
    
    private double alpha;

    public LaplaceScorer(IndexReader reader, String field,
            double realWordLikelyhood, BytesRef separator, double alpha) throws IOException {
        super(reader, field, realWordLikelyhood, separator);
        this.alpha = alpha;
    }
    
    @Override
    protected double scoreBigram(Candidate word, Candidate w_1) throws IOException {
        SuggestUtils.join(separator, spare, w_1.term, word.term);
        return (alpha + frequency(spare)) / (alpha +  w_1.frequency + vocabluarySize);
    }

    @Override
    protected double scoreTrigram(Candidate word, Candidate w_1, Candidate w_2) throws IOException {
        SuggestUtils.join(separator, spare, w_2.term, w_1.term, word.term);
        long trigramCount = frequency(spare);
        SuggestUtils.join(separator, spare, w_1.term, word.term);
        return (alpha + trigramCount) / (alpha  +  frequency(spare) + vocabluarySize);
    }


}
